Determining geotechnical, geophysical and geochemical properties of the seabed is an essential part of site assessment for offshore exploration and construction projects such as oil and gasfield platforms, anchorages, pipe and cable laying, wind energy and marine current turbine towers. Soil properties profoundly influence the design and performance of foundations for seabed structures, while detection of shallow gas is important for geohazard assessment during seabed operations or for hydrocarbons exploration potential of a site.
Soil properties are commonly measured using seabed penetrometers, deployed by various means including ‘wireline’ drillstring, coiled tubes, anchored seabed frames and remotely operated seabed platforms. Different types of apparatus are used according to the type of soil properties being investigated, for example the standard cone penetrometer test is suited for medium to high strength soils, the ball penetrometer for soft soils and the vane shear test and T-bar test for measurement of cohesive soils. In the case of geochemical measurements, sensing apparatus is currently used only above the seafloor via a towed submersible or a remotely operated vehicle, or via wireline deployment from a surface vessel into a borehole. Scientific investigation of the seabed often requires a wide range of instrumentation sensors to be deployed into a borehole. Increasingly, there is a trend for such seabed investigations to be performed at greater depth, in deep and ultra-deep water.
In situ seabed measurement apparatus commonly relies on wired electrical connections between the downhole probe and the seabed equipment or surface vessel for power supply and for data transmission to provide real time analysis and display. In deep water situations, such wireline systems are often deployed from relatively large drillships, floating platforms or dedicated survey vessels, all of which are expensive to operate. Some cheaper methods deploying ‘over-the-side’ apparatus are known, in which the seabed equipment is powered by a hydraulic umbilical or a battery pack, however these tend to have limited capability in their operating water depth or seabed penetration depth. Moreover, each type of measurement apparatus is currently used as a dedicated single-purpose device, with the disadvantage of little commonality in hardware and handling requirements.
It would thus be advantageous to provide a ‘universal’ instrumentation probe (UIP) of standardised configuration to which a variety of in situ measurement devices can be connected interchangeably. Such a UIP device would desirably transmit measurement data signals in real time as well as provide in situ data logging and means for remotely retrieving the logged data.
The advent of portable remotely operated seabed platforms with multi-use drilling, sampling, testing and measurement capabilities offers the flexibility to carry a range of in situ probes that can be deployed quickly and interchangeably according to geotechnical needs. However, such platforms that rely on remote makeup of a drillstring from individual lengths of pipe cannot use a wired electrical connection to the downhole apparatus. In this case the downhole apparatus is remotely powered by an attached battery pack.
A known alternative method of data transmission provides wireless communication via acoustic telemetry from the downhole apparatus. The electrical output signal from the measurement probe is converted to an acoustic signal which is transmitted through the drillstring to a receiving microphone coupled to the top of the drillstring. Down-hole acoustic telemetry presently operates only in one direction, from the probe to the seabed apparatus and not vice versa.
In current practice, probes and transmitters are switched on at the surface, at the launch of a deployment, and have no means to be remotely switched off or on. This is a severe disadvantage, as there is insufficient battery capacity to power the apparatus continuously for long deployment cycles, particularly in deepwater operations. Moreover, the built-in data logger may not have sufficient memory to avoid loss of data. In an overall deployment period extending possibly for days, a particular probe may only need to be powered up for short intervals. There is ample battery and memory capacity if the probe could be remotely switched on only when needed for taking in situ measurements. It would be further advantageous therefore to provide remote switching means to power the UIP on and off only as required.
Present acoustic methods of data transmission require a microphone to be coupled to the top of the drillstring. This is achieved simply by sandwiching the microphone housing between the end of the drill pipe and the feed chuck or anvil while applying downward force. With this method it is only possible to receive transmitted data during downward thrusting of the apparatus. In some instances however, such as measuring remoulded soil strength with a ball penetrometer, it would be advantageous also to receive data during upward movement of the apparatus. In other instances it would be advantageous to hold the drillstring in the feed chuck while taking measurements, for example to prevent possible run-away of a long drillstring under its own weight in very soft soils or to rotate a vane shear tool. This is not currently possible and requires the use of an auxiliary friction clamp.
To retrieve logged data in current practice it is necessary to bring the seabed probe assembly back to the surface, disassemble the probe and physically connect the memory module to an interface device for downloading. This can place inconvenient limitations on seabed operations and introduce significant delays in data recovery and verification.
It is the object of the present invention to provide means for alleviating one or more of the aforementioned disadvantages.
According to one aspect of the present invention there is provided a probe assembly suitable for use with apparatus for use in the investigation and/or analysis of an underwater floor of a body of water such as for example a seabed, the apparatus including a depth penetration device and an underwater floor testing tool, the probe assembly including a first coupling for operatively connecting the probe assembly to the depth penetration device and a second coupling for operatively connecting the probe assembly to the underwater floor testing tool, the probe assembly further including a signal processing module for processing information from the tool, a data transmission module for the transmission of data from the signal processing module, a power source for operating the data transmission module and the signal processing module and a switch module for selectively connecting from the power source to the data transmission module and signal processing module. The signal processing module may include an electronics module for processing signals from the tool into data and a data logging module for storing the data. The transmitter module may include an acoustic transmitter.
Preferably the switch module is a remotely actuatable device arranged to electrically connect and disconnect the power source to the processing module and transmitter module. The switch module may include a magnetic responsive switching device responsive to a magnetic field.
The probe assembly may further include a close range wireless communications device.
According to another aspect of the present invention there is provided apparatus for use in the investigation and/or analysis of an underwater floor of a body of water, the apparatus including a depth penetration device, a floor testing tool and a probe assembly as described above, the probe assembly being operatively connected to the depth penetration device and the tool, the apparatus further including a receiving microphone at an end of the depth penetrating device remote from the probe assembly and being acoustically coupled thereto via the depth penetrating device.
The receiving microphone may be contained in a liquid-filled enclosure which is pressure-equalised to the ambient water pressure at the seafloor. The receiving microphone may further be enclosed in a drive unit associated with the depth penetrating device.
According to yet another aspect of the invention there is provided a remotely activatable switch device suitable for use with a probe assembly as described above, the switch device including a switch element arranged in an electric circuit which includes two terminals, one being connectable to the power source and the other being connectable to the signal processing module and data processing module, the switch element being normally caused to adopt one of either a closed position in which the circuit is closed or an open position in which the circuit is opened, the switch being responsive to a magnetic field when in the vicinity thereof to cause the switch to adopt the open position.
The device may include a magnetically transparent housing, an electrically insulated switch body disposed within the housing, the switch element including a reed switch which is movable between the open and closed positions. The magnetic field comprises a magnet assembly mounted in the region of the underwater floor.
In a preferred form of the present invention there is provided a universal instrument probe assembly (UIP) including a remotely operated switch module, a battery power pack module, data conditioning, logging and transmitting modules, in combination with a range of seabed soil testing tools. The UIP is adapted to be connected to a drillstring or similar soil penetrating means, remotely deployed from seabed apparatus.
The UIP assembly may include a standard 36 mm diameter cylindrical housing. At the upper end it can be joined to similar sized extension rods or to a drill pipe adapter. The upper end of the UIP may also contain a transmitter which is capable of sending an acoustic data signal a distance of at least 100 m through an attached drill pipe. Attached below the acoustic transmitter module is a battery power pack module and a remotely operated switch module. The switch module may be electrically connected in series with the battery power pack and allows the transmitter and probe electronics to be powered on and off as required.
In one form, the switch module may include a magnetic switch wired in a ‘normally-closed’ position and arranged in a housing of magnetically transparent material such that the switch operates to an ‘open’ position when in proximity to a strong external magnetic field. The external magnetic field may be provided for example by rare earth permanent magnets located in a separate structure up to 200 mm laterally distant from the UIP switch module. When the switch module is assembled to the adjacent parts of the UIP, it is hermetically sealed against ambient water pressure to its rated depth.
The UIP assembly may also include a data logging module and an electronics module attached in series with the switch module. The electronics module may be electrically terminated with a multi-pin connector and can also be assembled onto an extension tube. The lower end of the extension tube may be adapted to attach a soil measurement tool, such as a cone penetrometer, a ball penetrometer, a vane shear tool or a gas sensor. A multi-core cable and matching connector inside the extension tube may be provided in order to link the electronics module to the soil measurement device, to supply power to the device and obtain measurement data signals. All connectors may be of underwater type suitable for the rated depth of the UIP assembly.
The length of the extension tube may be adapted according to the length of the particular type of attached soil testing device. In this way the overall length of the UIP tool assembly may be standardised to suit a single means of tool storage and robotic handling on the seabed platform. A variety of soil testing tools may thus be carried ready for deployment interchangeably, according to the soil conditions encountered.
In some applications such as, for example when used with a downhole gas sensor probe, it may be advantageous to connect drilling fluid or flushing water to the measurement probe. For this purpose the extension tube is of larger diameter than the UIP and may attach directly to the drill pipe adapter near the upper end of the UIP instead of to the electronics module at the lower end of the UIP. The extension tube thus encloses the UIP over its length with a small radial clearance to form an annular passage. Through this passage flushing water may be pumped from the drillstring to the sensor at the lower end of the extension tube.
In a further variation the UIP assembly may include an outer protection tube which normally encloses the vanes of a vane shear tool attachment but retracts when the vane tool is pushed into cohesive soil.
According to one example of the method of use of the invention, prior to launch from the surface vessel the seabed platform is prepared with a range of in situ testing and measurement tools, each assembled to a UIP. Typically the tool assemblies are stored systematically in a rack or magazine from which they can be remotely selected and deployed into a borehole via a robotic loading mechanism. The storage magazine is provided with permanent magnets located in proximity to the switch modules that are part of the UIP.
In the presence of the strong magnetic field the switch in a tool assembly is held in the open state and the tool remains powered down. The tool is powered up only while it is removed from the magazine for individual downhole use, when the switch reverts to the closed state in the absence of the strong magnetic field. In this way battery energy is drained only while the tool is being actively used, otherwise there may be insufficient battery capacity to last the full duration of a seabed operations cycle.
Whenever the UIP is powered up the measurement signals from the attached probe are processed by the electronics module into a digital data stream which is logged into the memory module. With the tool assembly attached to the drillstring the data stream is transmitted wirelessly from the borehole to the seabed platform by means of the acoustic transmitter in the UIP and the receiving microphone coupled to the top of the drillstring. From the seabed platform the data stream is further conveyed in real time to an operator on the surface vessel via electrically wired, fibre optic or other suitable means.
In a further aspect of the invention the UIP memory module may include a wireless communications device and an aerial or alternatively an electromagnetically transparent window, sealed to withstand hydrostatic pressures in a deepsea environment and allowing radio or magnetic signals to be transmitted and received. It is well known that radio signals are rapidly attenuated in seawater and that undersea radio communication is not practical over much distance. However it is possible to transmit over short distances (tens of millimeters). Magnetic induction communications is another suitable wireless technology for close range underwater data transfer. In this case a radiating coil transmits a magnetic field, with typical data rates up to 200 kbits/s. Therefore by fixing a similar communications device to the seabed apparatus in a position where the memory module may be brought into close proximity by a robotic tool handling mechanism, it is possible to establish two-way data transfer.
A number suitable wireless communications protocols exist, including those based on the IEEE802.11 standards, operating in the ISM (Industrial Scientific Medical) band at 2.4 GHz. These include proprietary protocols known under trademarks such as Bluetooth and AirPort, which commonly support data rates to 54 Mbit/s. The fixed communications device on the seabed apparatus may be connected by electrical wiring, optical fibre or by a combination of means to a surface operating station. Data downloading may thus be accomplished remotely from the UIP memory module while on the seabed. Alternatively if the UIP is brought to the surface, wireless downloading may be quickly accomplished using conventional communications-enabled computer equipment.
According to a further aspect of the invention there is provided an improved microphone configuration which allows the acoustic data signal to be received during both downward and upward movement of the drillstring in the seabed drilling platform. The drillstring water seal in the rotation unit and chuck assembly is adapted to include a microphone assembly in a separate chamber, while providing a path for the drilling fluid to pass to the drillstring.
The water seal may comprise a hollow shaft arranged to seal at the lower end into the top of the drill pipe while the drill pipe is gripped in the rotary chuck. The water seal shaft may pass up through a rotation drive unit to a rotary seal, commonly referred to as a water coupling or water swivel. The water coupling provides a non-rotating connection point for drilling fluid to be pumped via the water seal shaft through the rotation unit to the drillstring.
A small diameter connecting tube may pass from the microphone chamber through the bore of the water seal shaft and extends through the water coupling. The connecting tube encloses a wire that carries the output signal from the microphone to a single-contact rotary joint at the top of the water coupling. The microphone chamber, connecting tube and rotary joint are fully oil filled and pressure balanced to ambient conditions via connection to an external pressure compensator.
The microphone assembly may include a face plate with attached piezo crystals and resonant mass. The face plate cam forms the lower element of the water seal assembly and includes a spigot which aligns and acoustically couples the water seal assembly to the top face of the drill pipe.
To provide required acoustic coupling sensitivity the microphone face plate is preferably decoupled from the large mass of the rotation unit by means of a resilient compression washer placed between the face plate and the attachment flange of the rotation unit.
For operation of the enclosed microphone, the face plate is pressed in firm contact with the drillstring by applying downward force (bit weight) with the drill string held by a fixed lower clamp. The resilient washer is compressed axially and can be locked in this state by actuating the rotary chuck to grip the top of the drillstring. The compression force in the resilient washer thus holds the microphone face plate in contact with the top of the drillstring regardless of upward or downward movement of the drillstring in the borehole. Movement of the drillstring is positively restrained at all times either by the rotary chuck or the fixed rod clamp.
In addition to receiving measurement data from the UIP tool assembly during soil testing operations, the built-in microphone may also allow an operator to remotely ‘listen’ to rotary drilling operations on the seabed, thus providing another source of information for interpretation and control of the cutting process.
Thus the present invention may provide for real time data transmission during downward, upward and rotational movement of the soil testing apparatus.